To date, two mammalian bombesin-like peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB), have been characterized. These two peptides are widely distributed in mammalian nervous system and GI tract; but, of greatest clinical importance, GRP is expressed in developing lung and in lung cancer. Previous studies from our laboratory have demonstrated that bombesin-like peptides can profoundly stimulate small airway development both in terms of size and number. This suggests that bombesin-like peptides may have therapeutic potential to stimulate lung development in highly premature infants. Studies both from our laboratory and other laboratories have also suggested that expression of GRP and GRP receptors in developing lung can be influenced by exposure to nicotine (i.e., from maternal cigarette smoking). Thus an important regulator of fetal lung development may be influenced by maternal smoking. To further examine this, we will examine the effects of in utero administration of nicotine, bombesin-like peptides, bombesin agonists and bombesin antagonists on lung development. Drugs will be administered via osmotic minipumps with catheters going to amniotic fluid, the fetal peritoneal cavity, or both. Pilot studies will determine the stability of bombesin-like peptides in amniotic fluid and the percent of administered peptide that is delivered to the lung. Next, the administered effects of peptides on lung development will be determined. This will be analyzed both by morphologic criteria (i.e., airway size, number and histology) and biochemical criteria (i.e., surfactant).